↑ I ↓ This specification defines Atom link relations for navigation between a resource and its versions. This specification defines a set of link relation types that may be used on Web resources for navigation between a resource and and other resources related to version control, such as past versions and working copies.

This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts.

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as “work in progress”.

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the BSD License.

I'd be good to mention ATOM somewhere in the title. Also, both the
abstract and the introduction are extremely terse, to the point where
it's hard to understand what technologies/protocols this applies to.

↑ I This specification defines link relations that may be used on a resource that exists in a system that supports versioning to navigate among the different resources available, such as past versions. This specification defines a set ot link relation types that may be used on Web resources that exist in a system that supports versioning to navigate among the different resources available, such as past versions and working copies. ¶

These link relations are used in the AtomPub ([RFC5023]) bindings of the "Content Management Interoperability Services" (CMIS). See Section 3.4.3.1 of [CMIS] for further information.¶

When a resource is put under version control, it becomes a "versioned resource". Many servers protect versioned resources from modifications by considering them "checked in", and by requiring a "checkout" operation before modification, and a "checkin" operation to get back to the "checked-in" state. Other servers allow modification, in which case the checkout/checkin operation may happen implicitly.

When a versioned resource is checked out and then subsequently checked in, the version that was checked out becomes a "predecessor" of the version created by the checkin. A client can specify multiple predecessors for a new version if the new version is logically a merge of those predecessors. The inverse of the predecessor relation is the "successor" relation. Therefore, if X is a predecessor of Y, then Y is a successor of X.

A "checkin" is an operation on a working copy that creates a new version of its corresponding versioned resource.

Note: the operations for putting a resource under version control, and for checking in and checking out depend on the protocol in use and are beyond the scope of this document; see [CMIS], [RFC3253] and [JSR-283] for examples.¶

When included on a versioned resource, this link points to a resource containing the latest (e.g., current) version.¶

The latest version is defined by the system. For linear versioning systems, this is probably the latest version by timestamp. For systems that support branching, there will be multiple latest versions, one for each branch in the version history.¶

Automated agents should take care when these relations cross administrative domains (e.g., the URI has a different authority than the current document). Such agents should also take care to detect circular references.¶

Care should be applied when versioned resources are subject to differing access policies. In this case, exposing links may leak information even if the linked resource itself is properly secured. In particular, the syntax of the link URI/IRI could expose sensitive information (see Section 16.2 of [RFC3253] for a similar consideration in WebDAV Versioning). Note that this applies to exposing link metadata in general, not only to links related to versioning.¶

WebDAV: for version-controlled resources, DAV:checked-in ([RFC3253], Section 3.2.1) or DAV:checked-out ([RFC3253], Section 3.3.1), depending on checkin state. For version resources, a successor version that itself does not have any successors.

JCR: the version node identified by the jcr:baseVersion property ([JSR-283], Section 3.13.2.5) for versionable nodes; for version nodes, a successor version that itself does not have any successors.

WebDAV: for version-controlled resources that are checked-out in place: the resource itself. For version resources: each resource identified by a member of the DAV:checkout-set property (see [RFC3253], Section 3.4.3).

The "Web Linking" specification ([draft-nottingham-http-link-header]) generalizes Atom link relations, and also re-introduces the HTTP "Link" header as a way to expose link relations in HTTP responses. This will make it possible to expose version links independently from a specific vocabulary, be it the Atom Feed Format ([RFC4287]) or WebDAV properties ([RFC3253]).¶

For instance, a response to an VERSION-CONTROL request ([RFC3253], Section 3.5) could expose newly created version-history and checked-in version as link relations:¶